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Research Papers

Stress Relaxation Behavior of Mandibular Condylar Cartilage Under High-Strain Compression

[+] Author and Article Information
M. Singh

Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045

M. S. Detamore1

Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045detamore@ku.edu

1

Corresponding author.

J Biomech Eng 131(6), 061008 (Apr 29, 2009) (5 pages) doi:10.1115/1.3118776 History: Received June 17, 2008; Revised January 20, 2009; Published April 29, 2009

During temporomandibular joint (TMJ) function, the mandibular condylar cartilage plays a prime role in the distribution and absorption of stresses generated over the condyle. Biomechanical characterization of the tissue under compression, however, is still incomplete. The present study investigates the regional variations in the elastic and equilibrium moduli of the condylar cartilage under high strains using unconfined compression and stress relaxation, with aims to facilitate future tissue engineering studies. Porcine condylar cartilages from five regions (anterior, central, lateral, medial, and posterior) were tested under unconfined compression. Elastic moduli were obtained from the linear regions of the stress-strain curves corresponding to the continuous deformation. Equilibrium moduli were obtained from the stress relaxation curves using the Kelvin model. The posterior region was the stiffest, followed by the middle (medial, central, and lateral) regions and the anterior region, respectively. Specifically, in terms of the equilibrium modulus, the posterior region was 1.4 times stiffer than the middle regions, which were in turn 1.7 times stiffer than the anterior region, although only the difference between anterior and posterior regions was statistically significant. No significant differences in stiffness were observed among the medial, central, lateral, and posterior regions. A positive correlation between the thickness and stiffness of the cartilage was observed, reflecting that their regional variations may be related phenomena caused in response to cartilage loading patterns. Condylar cartilage was less stiff under compression than in tension. In addition, condylar cartilage under compression appears to behave in a manner similar to the TMJ disc in terms of the magnitude of moduli and drastic initial drop in stress after a ramp strain.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(A) Superior view of a left porcine condyle, displaying the different regions of the condylar cartilage (A: anterior, M: medial, C: central, L: lateral, and P: posterior). The circles represent the locations from where cylindrical specimens of 5 mm diameter were prepared (shown to scale).

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Figure 2

Photograph of the custom-built bath and compression platen assembly. Shown here is the bath (1) to which the lower compression platen (2) was affixed. The upper compression platen (3) was attached to the movable crosshead that carried a load cell (4) of 10 N capacity. The temperature was controlled using an immersion heater (5) and a temperature probe (6), both connected to a temperature controller.

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Figure 3

Typical stress-strain response of a condylar cartilage specimen, when compressed to 50% strain. The example curve provided here belongs to a specimen from the posterior region. The curve demonstrates a nonlinear region extending to approximately 30% strain, followed by a linear region. The inset displays an enlarged view of stress-strain response for the initial strain values.

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Figure 4

(a) A typical stress relaxation response, illustrating a “rapid” relaxation phase followed by a more gradual “slow” relaxation phase. The specimen provided here was from the posterior region. (b) Kelvin model fit to determine the equilibrium modulus. The Kelvin model could not provide a close fit for the entire data, so the Kelvin model was fit to only the slow relaxation phase.

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